This invention relates to techniques for making joints in concrete pavement.
It is known to pour continuous long strips of pavement and then later to cut joints in the continuous pavement. This process is efficient in highway construction because it is efficient to pour the concrete in continuous strips but joints are needed in the long strips of concrete pavement for temperature related expansion or contraction, weight distribution onto the ground and the like. To cut the pavement, heavy vehicles including saws move across the pavement spaced at periodic intervals along the pavement. The saws are mounted to the underside of the heavy vehicles transverse to the direction of motion of the vehicles and make straight cuts partway through the pavement or in some occasions all the way through. When the cuts are made partway from the top surface toward the bottom surface through the concrete pavement, the pavement cracks from the end of the cut downwardly to its bottom surface.
It is also known to mix within the concrete along with the cement substitute filler materials. These filler materials are frequently waste materials that find disposal within the concrete such as, fly ash or calcine clay. Some of these substitute materials reduce the expansion and contraction of the concrete. Without these particles, the concrete will expand during aging and exert sufficient force against the surfaces at the cut portion to prevent the concrete from moving upwardly and downwardly as traffic passes over them. When some filler materials such as fly ash or calcine clay are mixed in with the concrete, the expansion during aging is reduced and movement at the joints continues.
In the prior art, to prevent excessive displacement and cracking due to the movement of the concrete at the joints, steel load transfer bars are used to hold the joint together at those points. This arrangement has the disadvantage of being expensive and increasing the cost of laying roadways.
Accordingly, it is an object of the invention to provide a novel technique for applying concrete pavement.
It is a further object of the invention to provide a novel technique for making joints in concrete pavement.
It is a still further object of the invention to provide a novel technique for making joints cut at an angle to the vertical so as to transfer pressure between concrete slabs on opposite sides of the joints in concrete roadways.
It is a still further object of the invention to provide novel equipment for making joints in concrete roadways that are at an angle to the vertical.
It is a still further object of the invention to provide a technique for reducing the cost of laying concrete pavement.
It is a still further object of the invention to provide a technique for reducing the cost of laying concrete pavement by eliminating the need for steel rods to transfer pressure.
In accordance with the above and further objects of the invention, concrete pavement is poured in a continuous strip. After the concrete has hardened, it is cut at a substantially constant angle of between 5 and 45 degrees from the vertical in a plane transverse to the longitudinal axis of the highway or other strip, which plane forms the angle between 5 and 45 degrees with the vertical. The cut is made from the surface of the pavement downwardly at the angle diverging from the vertical plane it intersects at the surface of the pavement of between 5 and 45 degrees (between 85 and 45 degrees from the horizontal surface of the pavement) and in the same general direction as the movement of traffic. With this arrangement, when traffic moves over the joint, the front wheels of the vehicles move from a first slab of concrete onto the top portion of a second slab of concrete at the surface cut and proceeds over the second slab as the cut gets deeper. Experience has shown that the first slab tends to move upwardly and this causes pressure at the joint from the first slab against the second slab at the angled cut. The second slab moves downwardly and this also presses the second concrete slab against the first slab at the cut joint to hold the surfaces compactly together. The pressure at the angle of the joint causes a wedging action and the slabs are forced to move laterally when pressed at the angled joint, thus maintaining contact between adjacent slabs. The cuts may extend at an angle either from the surface of the concrete all the way to the bottom of the concrete or may be cut only partway down such as a third of the way down or more and the remainder of the concrete simply cracks itself.
In addition to being cut at an angle with respect to the horizontal plane the concrete may be cut at an angle in a horizontal plane with the angle being with respect to a vertical plane taken across the length of the highway and the joint extending at the angle from one side of the highway to the other so that the wheels engage the concrete one wheel at a time as it moves forward. This has been done in the prior art. While the cut is preferably made at a constant angle of between 5 and 45 degrees from the vertical starting at the surface of the pavement and diverging downwardly, the angle can be changed as the cut gets deeper and larger angles can be used as long, as the principle of having the first and second slabs press against each other is maintained. Similarly, the cut may be in the direction against the flow of traffic although this is not preferred and can cause some movement of the slabs with respect to each other before the front wheels of the vehicles leave the first slab and press the second slab against the first slab. In the alternative, cuts may be made in opposite directions on alternate joints for convenience since this permits a continuous cut across the roadway without turning the saw around.
The cuts may be made using conventional sawing equipment available on the market or specially adapted adjustable equipment. In the conventional equipment, vehicles containing the saws that are vertically mounted, may be moved upwardly on to a ramp and fixed in place. When the front wheels are on a ramp and the back wheels against the roadway, the normally vertical saw blade will actually be at an angle to the surface of the concrete. It may then be rotated and moved downwardly as customarily done but will cut the concrete at an angle rather than in a substantially straight vertical plane. On the other hand, special equipment adjusted to change the angle of the blade may be used so as to not require the use of ramps.
As can be understood from the above description, the technique and equipment of this invention has the advantage of reducing the cost of making joints in a roadway and provide for joints that do not require steel rods and yet in a superior manner, reduce the amount of cracking and wear at the joints.